British author G.K. Chesterton argued that every act of blasphemy is a kind of tribute to God, because it is based on belief. "If anyone doubts this," he wrote, "let him sit down seriously and try to think blasphemous thoughts about Thor."

By the evidence of the New York Times bestseller list, God has recently been bathed in such tributes. An irreverent trinity -- Christopher Hitchens, Sam Harris and Richard Dawkins -- has sold a lot of books accusing theism of fostering hatred, repressing sexuality and mutilating children (Hitchens doesn't approve of male circumcision). Every miracle is a fraud. Every mystic is a madman. And this atheism is presented as a war of liberation against centuries of spiritual tyranny.

Proving God's existence in 750 words or fewer would daunt even Thomas Aquinas. And I suspect that a certain kind of skeptic would remain skeptical even after a squadron of angels landed on his front lawn. So I merely want to pose a question: If the atheists are right, what would be the effect on human morality?

If God were dethroned as the arbiter of moral truth, it would not, of course, mean that everyone joins the Crips or reports to the Playboy mansion. On evidence found in every culture, human beings can be good without God. And Hitchens is himself part of the proof. I know him to be intellectually courageous and unfailingly kind, when not ruthlessly flaying opponents for taking minor exception to his arguments. There is something innate about morality that is distinct from theological conviction. This instinct may result from evolutionary biology, early childhood socialization or the chemistry of the brain, but human nature is somehow constructed for sympathy and cooperative purpose.

But there is a problem. Human nature, in other circumstances, is also clearly constructed for cruel exploitation, uncontrollable rage, icy selfishness and a range of other less desirable traits.

So the dilemma is this: How do we choose between good and bad instincts? Theism, for several millennia, has given one answer: We should cultivate the better angels of our nature because the God we love and respect requires it. While many of us fall tragically short, the ideal remains.

Atheism provides no answer to this dilemma. It cannot reply: "Obey your evolutionary instincts" because those instincts are conflicted. "Respect your brain chemistry" or "follow your mental wiring" don't seem very compelling either. It would be perfectly rational for someone to respond: "To hell with my wiring and your socialization, I'm going to do whatever I please." C.S. Lewis put the argument this way: "When all that says 'it is good' has been debunked, what says 'I want' remains."

Some argue that a careful determination of our long-term interests -- a fear of bad consequences -- will constrain our selfishness. But this is particularly absurd. Some people are very good at the self-centered exploitation of others. Many get away with it their whole lives. By exercising the will to power, they are maximizing one element of their human nature. In a purely material universe, what possible moral basis could exist to condemn them? Atheists can be good people; they just have no objective way to judge the conduct of those who are not.

The death of God has greater consequences than expanded golf time on Sunday mornings. And it is not simply religious fundamentalists who have recognized it. America's Founders embraced public neutrality on matters of religion, but they were not indifferent to the existence of religious faith. George Washington warned against the "supposition that morality can be maintained without religion." The Founders generally believed that the virtues necessary for self-government -- self-sacrifice, honesty, public spirit -- were strengthened by religious beliefs and institutions.

None of this amounts to proof of God's existence. But it clarifies a point of agreement -- which reveals an even deeper division. Atheists and theists seem to agree that human beings have an innate desire for morality and purpose. For the theist, this is perfectly understandable: We long for love, harmony and sympathy because we are intended by a Creator to find them. In a world without God, however, this desire for love and purpose is a cruel joke of nature -- imprinted by evolution, but destined for disappointment, just as we are destined for oblivion, on a planet that will be consumed by fire before the sun grows dim and cold.

This form of "liberation" is like liberating a plant from the soil or a whale from the ocean. In this kind of freedom, something dies.